This application relates to the subject matter of U.S. application Ser. No. 08/131,977, filed Oct. 4, 1993, now U.S. Pat. No. 5,397,280, entitled "System Phasing of Overhead Cam Timing Chains."
The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in engine timing applications as well as in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle.
The invention relates to phasing of the chain assemblies and the sprockets to modify the impact noise spectrum and chordal action noise spectrum. Specifically, the invention includes the use of timing chains in conjunction with phased sprockets to alter the noise spectra in an engine timing system. The invention also includes the use of random chains in conjunction with phased sprockets to alter the noise spectra.
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power from the torque converter to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins received in a pair of apertures. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference.
Conventional silent chains typically include both guide links and inverted tooth links. The guide links are positioned on the outside edges of alternate sets of links. The guide links typically act to position the chain laterally on the sprocket. Guide links typically do not mesh with the sprocket.
The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and sprocket. Each inverted tooth link typically includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined at a crotch. The inverted tooth links are typically designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links or driving links contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks. The contacts between the links and the sprocket teeth can be of the type which provide a power transfer, or can be of the nature of an incidental contact, or can include root contact or side contact.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts. Rotation of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket mounted on the camshaft. The rotation of a camshaft is thus controlled by and dependent on the rotation of the crankshaft through the chain. A chain for an engine timing drive application is shown in U.S. Pat. No. 4,758,210, which is incorporated herein by reference.
A conventional chain drive may include a chain assembly of extended width in order to provide a chain of greater strength. Alternatively, two chain assemblies may be placed side-by-side between pairs of sprockets in order to achieve the equivalent power transmission results as a single extended width chain.
Engine timing systems conventionally include at least one driving sprocket located on the crankshaft and at least one driven sprocket located on the camshaft. Rotation of the crankshaft causes rotation of the camshaft through the chain and sprocket system.
The most basic conventional engine timing system typically includes a single sprocket on the crankshaft connected to a single sprocket on the camshaft, with the crankshaft sprocket having one-half the number of teeth of the camshaft sprocket. Such a camshaft typically controls the valve train operation through hydraulic lifters and rocker arms connected to the valve stems. The chain can be of a narrow width in construction, such as shown in U.S. Pat. No. 4,758,210, which is incorporated herein by reference.
A more complicated engine timing system of the prior art connects the crankshaft with two overhead camshafts by a pair of chains. The crankshaft includes two sprockets. Each chain is connected to a single sprocket on each of the two overhead camshafts. Typically, the chain systems will include tensioners on the slack side of each chain to maintain chain tension and snubbers on the tight side of each chain to control chain movement during operation.
More complicated engine timing systems are also utilized in the prior art. Such systems include timing systems having two (or dual) overhead camshafts for each bank of cylinders. The dual camshafts on a single bank can both be rotated by connection to the same chain. Alternatively, the second camshaft can be rotated by an additional camshaft-to-camshaft chain drive. The cam-to-cam drive chain can also include single or dual tensioners for chain control. All of these structures are known in various forms in the prior art.
Conventional timing systems of the prior art can also include more complicated structures than a single sprocket on the crankshaft driving a single sprocket on a camshaft. Some systems include an idler sprocket between the crankshaft and camshaft. One chain system drives the idler which in turn drives either single or dual overhead camshafts. The sizing of the idler gear is such as to allow different rotational speeds of the crankshaft and camshaft. For example, the crankshaft may rotate twice the speed of the crankshaft by the sizing of the sprockets for the chain and sprocket drive system.
Noise is associated with chain drives. Noise is generated by a variety of sources, but in silent chain drives it can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket and the mass of chain links contacting the sprocket at a particular moment or time increment.
The meshing impact sound is generally a periodic sound in chain drives. The impact sound is repeated with a frequency generally equal to that of the frequency of the chain meshing with the sprocket. The frequency is related to the number of teeth on the sprocket and the speed of the sprocket. The impact can produce sound having objectionable pure sonic tones.
Another cause of noise in chain drives is the chordal action of the chain and sprockets as the chain is driven about the sprockets. Chordal action occurs as the chain link enters the sprocket from the free chain. The meshing of the chain and sprocket at the chain mesh frequency can cause a movement of the free chain or span (the part of the chain between the sprockets) in a direction perpendicular to the chain travel but in the same plane as the chain and sprockets. This vibratory movement can also produce an objectionable pure sonic tone at the frequency of the chain mesh frequency or a derivative of it.
Many efforts have been made to decrease the noise level and pitch frequency distribution in chain drives of the silent chain variety to minimize the objectionable effects of the pure sonic tones. The problem of noise reduction in silent chain drives was addressed in U.S. Pat. No. 4,342,560 by changing the contacts between the link flanks of a silent chain and the sprocket teeth by having differently configured link flanks in different sets of the chain. By mixing links of differing flank configuration, U.S. Pat. No. 4,342,560 attempted to modify the pattern of sound emanating from the chain contacting the sprocket by altering the types of link configurations and thus altering the point and rhythm of contacts. A similar concept was used in U.S. Pat. No. 4,832,668. Each of these patents teaches the reduction of chain noise level by randomization of elements within the chain, such as link configuration or profile, or link aperture-to-flank spacing distance.
U.S. Pat. No. 4,915,675, which is incorporated herein by reference, utilized the same concept of modifying the pattern of sound emanating from the chain by altering the types of link configurations. That patent teaches the utilization of an asymmetrically shaped link form which is then oriented in two different directions in the chain assembly to alter the point and rhythm of chain to sprocket contacts.
Other attempts to alter the rhythm of contacts between the silent chain drive and the sprocket have focused on the modification of elements within the sprocket, such as the sprocket tooth profile or the spacing of the sprocket teeth on the sprockets. For example, U.S. Pat. No. 3,377,875 and U.S. Pat. No. 3,495,468, which are both incorporated herein by reference, teach modification of certain sprocket teeth or even elimination of some teeth in order to achieve noise reduction in contacts between the links of the silent chain and the sprocket teeth.
The present invention is directed to noise reduction by modification of the impact sound pattern and the chordal action sound pattern, which are generated by chain and sprocket contacts. The invention attempts to modify those sound patterns by various phasing relationships between the chain assembly and the sprockets. Phasing the chain and sprocket relationship can reduce the number of chain link teeth (or mass of chain) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket. Both of these phasing modifications, alone and in conjunction with the randomization of the chain and sprocket contacts, can alter the impact and chordal action generated sound patterns.
With regard to use of phasing relationships in the prior art, a manual transmission drive of the Saab 99 vehicle used three individual roller chains in parallel on three separate, spaced-apart sprockets. These roller chains differ from the inverted tooth chains of the present invention and have different power transmission and noise characteristics. The three identical roller chains were run in parallel with each chain and sprocket phased by 1/3 pitch relative to the adjacent chain and sprocket. This system is described in an August 1980 ASME paper entitled "Roller Chain as a Transfer Drive for the Automobile." A roller chain system with offset sprockets is also shown in U.S. Pat. No. 3,029,654.
Japanese published patent applications nos. 62-56141, 63-227318, 63-75516 and 1-51359 each describe phased or offset sprockets for use in transmission or in a transfer case for a four wheel drive vehicle. These publications do not disclose engine timing systems. Moreover, these prior art applications differ from the transmission and transfer case applications of the present invention in which phasing is utilized in conjunction with random or hybrid chains. The published Japanese applications teach the use of a "cancellation effect," which is developed by the particular spacing of two offset sprockets. The "cancellation effect" differs from randomization in its approach to the problem of chain noise. Cancellation relies on a pair of sprockets offset by 1/2 pitch in conjunction with two non-random chains. Each sprocket provides a repetitive pattern of discrete chain and sprocket contacts which are phased by 1/2 pitch and therefore act to "cancel" one another. In contrast, the random chain in the transmission embodiment of the present invention provides a random pattern of contacts between chain and sprocket. Randomization is inconsistent with the concept of cancellation through generation of a repetitive pattern of discrete contacts.
The Japanese prior art applications do not utilize phasing in conjunction with an engine timing system. Timing systems applications include load fluctuations and extreme center distances that differ dramatically from transfer case applications.
One embodiment of the present invention seeks to provide a phasing relationship by using a silent chain construction having randomization achieved by use of a combination of single toe inverted tooth links with conventional two toed inverted tooth links in a single chain assembly or in a double chain assembly. The combination of single toe links and two toed links can randomize or alter the pattern of link and sprocket tooth contacts in the chain and sprocket assembly. The single toe links are provided in a chain assembly with a split sprocket having a phased relationship, or a non-phased relationship.
Prior art chains have utilized single toe links, but not in a dual chain or phased chain assembly relationship. For example, U.S. Pat. No. 959,046 discloses a single toe guide link. However, the guide links act only to maintain the chain assembly on the sprockets. The guide links do not provide direct power transfer to or from the sprocket and thus do not impact the sprocket at the chain mesh frequency. Hence, the use of single toe guide links does not effect the noise spectrum produced by the sprocket tooth contacting links or articulating links.
U.S. Pat. No. 579,742 discloses a chain with single toe links that are located slightly off-center. The links engage the sprocket through antifriction balls that are trapped in sprocket cavities. All of the links of the chain have single toes.
U.S. Pat. No. 637,056 shows a chain with single toe links that are substantially centrally located. The patent discloses a chain having cylindrical sprocket teeth that come into contact with the link toe at its base. The contact of the link and the cylindrical toe is intended to occur on both sides of the toe. All of the links of the chain are single toe.
As part of the phased chain and sprocket assembly, the present invention also provides a modified sprocket construction. The modified sprocket may be used with the random or hybrid chain assemblies, or with the single toe link chain assembly, to provide the phased chain and sprocket relationship. The single toe links and sprocket are utilized in an attempt to modify the pattern of contacts between the chain and the sprocket and minimize problems of interference of the links with the sprocket as the links move off of the sprocket teeth.